The central theme of this Program Project revolves around the genetic toxicology of DNA adducts. The chemistry and biology of environmental mutagens, including aromatic amines, benzo(a)pyrenes food mutagens, and products of oxidative DNA damage are being investigated. Novel biological systems are employed that reflect the mutagenic specificity of a single DNA adduct and reveal fundamental relationships between structure and biological activity. This information enables mechanisms of mutagenesis and DNA repair to be elucidated at the molecular and cellular level. The focus of this Program on environmental mutagenesis remains unchanged. Studies of oxidative DNA damage will be expanded and a project on mitochondrial DNA damage has been included. Projects include 1. Synthesis of oligodeoxynucleotides bearing mutagens as site-specified adducts and analysis of oxidative DNA damage; 2. Mechanisms of chemical mutagenesis and repair of DNA adducts; 3. Mitochondrial DNA damage and repair; 4. Response to DNA damage of eukaryotic DNA polymerases alpha, beta, and epsilon and 5. Structure, protein recognition, and energetics of damaged DNA. A primary objective of Project 1 is to synthesize oligodeoxynucleotides, modified site-specifically with DNA adducts, which can be used for biological research and structural studies. Studies will be undertaken on the mechanism of action of DNA repair enzymes. Mass spectroscopic methods will be applied to the quantitative analysis of oxidative damage. Project 2 proposes to establish the effect of sequence context on translesional synthesis. Mechanisms by which DNA repair enzymes recognize and repair damaged DNA will be explored. In Project 7, novel methods will be used to quantify oxidative damage to mitochondrial DNA and to explore its consequences. The goals of Project 4 are to compare the action on chemically modified template-primers and to test explicit biological hypothesis based on in vitro mechanistic studies. In Project 6 three- dimensional structures of DNA adducts and lesions will be analyzed with respect to molecular events encountered during mutagenesis. Computational methods will be developed to predict patterns by which repair enzymes recognize damaged DNA. The Core component of the Program consists of experienced technical staff who prepare the chemically modified oligodeoxynucleotides and perform mass spectrophotometric analyses.